/* @(#)e_atan2.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 *
 */

#include "math.h"
#include "float.h"

static volatile double
tiny  = 1.0e-300;
static const double
zero  = 0.0,
pi_o_4  = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */
pi_o_2  = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */
pi      = 3.1415926535897931160E+00; /* 0x400921FB, 0x54442D18 */
static volatile double
pi_lo   = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */

double
__ieee754_atan2(double y, double x)
{
    double z;
    int k,m,hx,hy,ix,iy;
    unsigned int lx,ly;

    EXTRACT_WORDS(hx,lx,x);
    ix = hx&0x7fffffff;
    EXTRACT_WORDS(hy,ly,y);
    iy = hy&0x7fffffff;
    if(((ix|((lx|-lx)>>31))>0x7ff00000)|| /*lint !e501*/
       ((iy|((ly|-ly)>>31))>0x7ff00000))    /* x or y is NaN */ /*lint !e501*/
       return x+y;
    if((hx-0x3ff00000|lx)==0) return atan(y);   /* x=1.0 */
    m = ((hy>>31)&1)|((hx>>30)&2);    /* 2*sign(x)+sign(y) */

    /* when y = 0 */
    if((iy|ly)==0) {
        switch(m) {
        case 0:
        case 1: return y;     /* atan(+-0,+anything)=+-0 */
        case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
        case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
        }
    }
    /* when x = 0 */
    if((ix|lx)==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;

    /* when x is INF */
    if(ix==0x7ff00000) {
        if(iy==0x7ff00000) {
        switch(m) {
            case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
            case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
            case 2: return  3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
            case 3: return -3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
        }
        } else {
        switch(m) {
            case 0: return  zero  ;    /* atan(+...,+INF) */
            case 1: return -zero  ;    /* atan(-...,+INF) */
            case 2: return  pi+tiny  ;    /* atan(+...,-INF) */
            case 3: return -pi-tiny  ;    /* atan(-...,-INF) */
        }
        }
    }
    /* when y is INF */
    if(iy==0x7ff00000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;

    /* compute y/x */
    k = (iy-ix)>>20;
    if(k > 60) {             /* |y/x| >  2**60 */
        z=pi_o_2+0.5*pi_lo;
        m&=1;
    }
    else if(hx<0&&k<-60) z=0.0;     /* 0 > |y|/x > -2**-60 */
    else z=atan(fabs(y/x));        /* safe to do y/x */
    switch (m) {
        case 0: return       z  ;    /* atan(+,+) */
        case 1: return      -z  ;    /* atan(-,+) */
        case 2: return  pi-(z-pi_lo);/* atan(+,-) */
        default: /* case 3 */
                return  (z-pi_lo)-pi;/* atan(-,-) */
    }
}

double atan2(double y, double x)
{
    return __ieee754_atan2(y, x);
}
